A navigation system typically used in a vehicle determines a navigation route toward an inputted destination of a travel for navigating a user/driver of the vehicle. That is, for example, the navigation system disclosed in Japanese Patent Document JP-A-H5-224601 determines the navigation route toward the destination of the travel by using a cost minimizing method based on the Dijkstra method or the like. In the navigation system disclosed in the above document, the cost of the navigation route is calculated and evaluated by adding plural types of cost with its weighting factor multiplied thereon.
The Japanese Patent Document JP-A-H5-224601 is an example of a car navigation system, and the parameters for cost calculation includes a distance of travel, an average travel time, a width of a road and the like. The weighting factors for those parameters can be adjustably changed for prioritizing a specific characteristic of route navigation represented by those parameters.
The navigation system of the above patent document calculates a navigation route by using an evaluation function, and the navigation route having the minimum evaluation value (a “cost” of the navigation route) is presented to the user as a first option among the plural route selections. Then, the weighting factor of the respective parameters is adjustably changed for rearrangement of the cost calculation priority when the user selects an alternative route (i.e., a route different from the first option). In other words, the weighting factors of the parameters are changed so that the cost of the selected navigation route is calculated as a minimum in comparison to the cost of the other navigation routes. In this manner, route selection of the navigation system is gradually tailored to reflect the user's preference such as a distance first selection, a travel time first selection, an ease of travel selection or the like.
Though the navigation system of the above patent document does reflect the user's preference on the route selection, the user's preference itself does change depending on, for example, the day of the week, the time of the day or the like. That is, the user may select the travel time first selection on weekdays to quickly get to a destination of the travel while the user select the ease of travel selection on the weekend at the cost of the travel time. Other cases for change of the selection may be that the ease of travel is preferred when the user is going home in the evening, while the shorter travel time is preferred for other time of the day.
The user's preference may be changed according to the context of the travel specifically for a short time range of the travel such as a specific time slot of the day, the day of the week or the like. However, the navigation system in the above disclosure does not take that kind of changing user preference into account. That is, the navigation system fails to reflect the user's preference when, for example, the time slot of the travel does not match the expectation/assumption of the navigation system. The user of a handheld type navigation system may encounter the same problem when the navigation system adopts the same navigation algorithm.